USB PD Explained: How It Works and Choosing GaN Chargers and Cables
A practical guide to how USB PD works, its standards, and choosing GaN chargers and USB-C cables.
What Is USB PD
USB PD stands for USB Power Delivery. It is a power supply standard developed by USB-IF. It is a system for using USB, originally for data communication, for power delivery as well. Conventional USB power was centered on 5V with low output. With USB PD, up to 240W can be supplied. It covers a wide range from smartphones to laptop computers. It is the de facto standard for charging portable devices. Specifications are also published in the official USB-IF information (https://www.usb.org/usb-power-delivery).
How It Works: Negotiation and PDO
The core of USB PD lies in negotiation between devices. Connection starts at a safe 5V voltage. Devices then notify each other of their capabilities over the CC wire. The charger presents a voltage-current table called PDO. The sink selects and requests its preferred PDO. The voltage switches to a higher level only after an agreement is reached. High voltage is never applied without agreement. This procedure is what prevents device damage. Communication uses the CC pins of the USB-C connector. PD negotiation does not work over conventional USB-A. As a rule, USB-C on both ends is required for PD use. Exceptions exist for conversion use with USB-C on one end. For output stability, USB-C on both ends is the reliable choice.
Examples of PDOs are as follows.
- 5V 3A: for small devices and initial negotiation
- 9V 3A: for fast charging smartphones
- 12V 3A: for tablets and small peripherals
- 15V 3A: for mid-range output for mobile PCs
- 20V 5A: for high-performance laptops Devices select the optimal value from the supported PDOs. The more PDOs a charger offers, the higher its compatibility. With insufficient PDOs, charging may remain slow.
Evolution of the Standard: SPR, EPR, and PPS
USB PD 2.0 established the framework for up to 100W. USB PD 3.0 advanced device coordination and granularity. The current mainstream is USB PD 3.1. Version 3.1 introduces two categories: SPR and EPR. SPR covers the range up to 100W at a maximum of 20V 5A. EPR adds 28V, 36V, and 48V. EPR is capped at 48V 5A for 240W. It targets high-output laptops and workstations. It is defined in the USB-IF specification documents (https://www.usb.org/document-library/usb-power-delivery).
PPS is a function that finely varies voltage. It adjusts from 3.3V to 21V in 20mV steps. It helps suppress heat generation and protect battery life. It is required by some smartphones in South Korea and the United States. Samsung Super Fast Charging relies on PPS. Google Pixel fast charging also uses PPS. Output will not reach full levels with chargers that do not support PPS. AVS is a variable specification that extends PPS. Check product specification sheets to confirm support.
Output Guide: Power Needs by Device
Power requirements vary by device. Knowing the guidelines makes selection easier.
- Wireless earbuds and watches: 5W to 15W
- Smartphones: 18W to 45W
- Tablets: 20W to 45W
- Thin laptops: 45W to 65W
- High-performance laptops: 65W to 140W
- Handheld game consoles: 39W to 65W Matching PDOs is more important than actual power consumption. For example, a 65W charger suits a device that supports 20V. A charger limited to 15V will not charge at full speed. Always check the voltage required by the sink device.
How to Choose a GaN Charger
GaN is a semiconductor using gallium nitride. It has lower losses than conventional silicon. It suits high-frequency operation and allows smaller components. For the same output, the housing can be smaller with less heat. It pairs well with multi-port products. The following points are useful for selection.
- Maximum output when using a single port
- Power distribution when using multiple ports simultaneously
- Supported PDO and PPS ranges
- Housing size and plug shape
- Availability of temperature control and protection circuits Some products rated at 65W for a single port drop to 45W during simultaneous use. Total output and per-port output are different things. Check the output distribution table on the product page. Foldable plugs offer excellent portability. Fixed plugs are more stable for stationary use. Ensure space for heat dissipation during use. Avoid continuous high loads in enclosed spaces.
Practical examples for different uses are shown below.
- For business trips: compact 65W-class model with two ports
- For stationary home use: multi-port model of 100W or more
- For high-performance machines: 140W-class model supporting EPR The MacBook Pro that receives 140W requires PD 3.1 support. Apple’s technical documentation (https://support.apple.com/ja-jp/HT212575) also outlines the conditions for 140W power delivery. It is safest to check the charger output specified for your device.
How to Choose a USB-C Cable
Cables also directly affect output. The internal eMarker declares its capabilities. An eMarker is an identification chip built into the cable. Chargers and devices also refer to eMarker information. Output is limited when using a cable with insufficient capability. The categories are as follows.
- Up to 60W: 3A-compatible products
- Up to 100W: 5A-compatible products with eMarker
- Up to 240W: EPR-compatible products with eMarker An EPR-compatible cable is required for 240W charging. 240W negotiation will not succeed with a 100W cable. The longer the cable, the greater the voltage drop. Watch for heat and losses with cables over 2m. Thick power-only cables are cumbersome to handle. For portable use, a 100W cable around 1m is easy to handle.
Data performance and power delivery performance are separate metrics. Some USB 2.0-compatible products can still deliver 100W. USB4 or Thunderbolt support is required for video output. For charging only, the communication standard does not matter. Also check the durability of the jacket. Silicone jackets are flexible and tangle-resistant. Nylon braiding resists abrasion. If a cable is damaged, it is safer to stop using it for high-load applications.
Safe Use and Compatibility Notes
USB PD is highly safe thanks to its negotiation mechanism. Still, there are operational precautions. Heat can cause output to drop or stop. Poor contact between the charger and cable causes heat. Clean power connections where dust has accumulated. Avoid cheap products that fall outside the standards. USB-IF certified products have undergone interoperability testing. The presence of a certification logo is one factor in judging quality. Choose products for the domestic market bearing the PSE mark. Parallel imports from abroad may have different plug shapes. Continuous use of a conversion adapter increases contact resistance. Direct connection is more stable for stationary setups. Power supply limits are lower on aircraft and in vehicles. In such cases, sink devices may operate with reduced requests.
Editorial Opinion
The editorial team sees the supported PDO and PPS ranges as more important than the rated output figure. For laptop use, 65W or more and PPS support are the deciding criteria. Maximum output on a single port and distribution during simultaneous multi-port use should also be checked. The pitfall in the field lies in mismatched cable and charger combinations. Even with a 240W-compatible charger, output will be limited with a cable without an identification chip. Output drops due to heat and heat dissipation conditions during use also tend to be overlooked. The future direction lies in the spread of PD 3.1 EPR and miniaturization of high output. Consolidation to single-cable USB-C power for laptops and peripherals will progress. With next-generation semiconductors, 140W-class models will become the standard for portable use.
References
Frequently Asked Questions
- How can I tell if a device supports USB PD
- Check the charger and device specification sheets for USB PD, PD 3.0, or PD 3.1 markings. If the PDO list includes 9V, 15V, or 20V, it supports PD. For cables, eMarker support and maximum current ratings are the guide.
- What is different about a GaN charger
- Gallium nitride elements reduce power loss and make miniaturization easier. Even at the same 65W, the housing is smaller and heat is suppressed compared with conventional models. It is also advantageous for maintaining output on each port in multi-port products.
- Is it safe to charge a smartphone with a 100W charger
- It is safe. USB PD determines the appropriate voltage and current through negotiation between devices. Even if the charger's maximum is large, current beyond the device's request will not flow. If the PDOs include a compatible range, no slowdown will occur.
- What is required for 240W charging
- The charger, cable, and device must all support EPR. Use a cable clearly marked as 240W-compatible. Whether the PDOs list 28V or higher is the deciding factor.
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